The invention relates generally to semiconductor integrated circuits, and more particularly, to an apparatus and method for fabricating a spherical-shaped semiconductor device.
Conventional semiconductor devices, or "chips," are formed from a flat surface semiconductor wafer. The semiconductor wafer is first manufactured in a semiconductor material manufacturing facility and is then provided to a fabrication facility. At the latter facility, several layers are processed onto the semiconductor wafer surface. Once completed, the wafer is then cut into one or more chips and assembled into packages. Although the processed chip includes several layers fabricated thereon, the chip still remains relatively flat. One processing step that is performed in the fabrication facility is thermal diffusion. Traditional thermal diffusion is based on three process steps. First of all, a doping oxide is deposited on the wafer. Next, thermal diffusion is performed on the wafer substrate, typically at a temperature between 900.degree. C. to 1200.degree. C. to prevent warpage and detrimental stress to the wafer. After thermal diffusion, the doping oxide is removed. The depth of diffusion depends on several factors, including the crystal orientation of the substrate. On a flat wafer, the crystal orientation is relatively consistent.
In co-pending U.S. Pat. No. 5,955,776, filed on May 16, 1997, assigned to the same assignee as the present application and hereby incorporated by reference, a method and apparatus for manufacturing spherical-shaped semiconductor integrated circuit devices is disclosed. Being spherical-shaped, the crystal orientation of the devices differs for each portion of the device. The present invention is specific to an apparatus and method for performing a consistent, high-temperature diffusion on devices such as those that are spherical in shape.